The objective of this project is to study the reaction of thymus derived lymphocytes (T cells) to cell surface antigens. Within this objective we will examine the specificity, action and efficiency of Vitamin A derivative (Retinoids) in stimulating cell mediated immune reactions. The effects of these compounds on macrophages, antibody dependent cell mediated cytoxicity, natural killer cells as well as cytoxic T cells will be analyzed in various in vitro model systems. The efficiency of retinoids to stimulate cell mediated cytotoxicity will also be evaluated in in vivo tumor models with the goal to examine the usefulness of these drugs to suppress tumor growth by stimulating immunity. Our second objective is to explore whether the thymus is required for normal differentiation of T cells. In particular, the question will be analyzed whether T cells can proliferate and mature from prothymocytes in the absence of a thymus, and whether such T cells have normal response patterns. H-2 restriction of T cells from nude mice which matured in the absence of a thymus will be examined by assaying their function in T-B cooperation and possibly cell mediated cytotoxicity. Our third objective is to examine the cell surface markers and specificity of natural killer cells which we have been growing from normal spleen cell populations and which can be cloned in conditioned media. These cloned cell lines will also be tested in in vivo models for their tumor suppressive properties.